zfs discuss - Sep 2009 - associating an unmodified clone file with an origin snapshot

The context is a file in a dataset cloned from a snapshot.
If the file has not been modified since the clone was created,
I''d like to ascribe to the file attributes associated with
the origin snapshot.

    1)	Is it feasible to determine from the vnode relating to
	the clone file if that file is unmodified from the origin?
	(I''m hoping this can be as simple as verifying that the
	file uses the same data blocks as it did in the snapshot.)

    2)	Could modifications of other files in the clone dataset
	make the "unchanged" status of an unmodified file more
	difficult to verify?

					Thanks	-JZ